The next great telecom revolution phần 4

56 NUTS AND BITS—TELECOM HARDWARE, SOFTWARE, AND MORE Lidija Sekaric, now a researcher at IBM’s Watson Research Center in Yorktown Heights, New York, worked with Cornell graduate student Keith Aubin and undergraduate researcher Jingqing Huang on the new nanoguitar, which is about five times larger than the original but still so small that its shape can only be seen in a microscope. Its strings are really silicon bars, 150 by 200 nm in cross-section and ranging from 6 to 12mm in length (a micrometer is one-millionth of a meter; a nanometer is a billionth of a meter, the length of three silicon atoms in a row). The strings vibrate at frequencies 17 octaves higher than those of a real guitar, or about 130,000 times higher. The researchers recently observed that light from a laser could cause prop-erly designed small devices to oscillate, and this effect underlies the nano-guitar design. The nanoguitar is played by hitting the strings with a focused laser beam.When the strings vibrate, they create interference patterns in the light reflected back, which can be detected and electronically converted down to audible notes. The device can play only simple tones, although chords can be played by activating more than one string at a time. The pitches of the strings are determined by their length, not by their tension as in a normal guitar, but the group has “tuned” the resonances in similar devices by apply-ing a direct current voltage. “The generations of researchers to come can aim to play more complex pieces,” says Sekaric. “This goal would indeed improve the science and tech-nology of NEMS by aiming for integrated driving and detection schemes as well as a wide range of frequencies produced from a small set of vibrating elements.” Most of the devices the group studies don’t resemble guitars, but the study of resonances often leads to musical analogies, and the natural designs of the small resonant systems often leads to shapes that look like harps, xylophones, or drums.The guitar shape was,Craighead Sekaric says,“an artistic expression by the engineering students.” Sekaric notes that “a nanoguitar, as something close to almost everybody’s understanding and experience, can also be used as a good educational tool about the field of nanotechnology, which indeed needs much public education and outreach.” The ability to make tiny things vibrate at very high frequencies offers many potential applications in electronics. From guitar strings on down, the fre-quency at which an object vibrates depends on its mass and dimensions. Nanoscale objects can be made to vibrate at radio frequencies (up to hundreds of megahertz) and so can substitute for other components in electronic cir-cuits.Cell phones and other wireless devices,for example,usually use the oscil-lations of a quartz crystal to generate the carrier wave on which they transmit or to tune in an incoming signal.A tiny vibrating nanorod might do the same job in vastly less space, while drawing only milliwatts of power. Research by the Cornell NEMS group has shown that these oscillations can be tuned to a very narrow range of frequencies—a property referred to in elec-tronics as “high Q”—which makes them useful as filters to separate signals of different frequencies.They also may be used to detect vibrations to help locate STORAGE 57 objects or detect faint sounds that could predict the failure of machinery or structures. As the nanoguitar shows, NEMS can be used to modulate light, meaning they might be used in fiber-optic communications systems. Such systems currently require a laser at each end for two-way communication. Instead, Craighead suggests that a powerful laser at one end could send a beam that would be modulated and reflected back by a far less expensive NEMS device. This could make it more economical to run fiber-optic connections to private homes or to desktop computers in an office. 2.14 STORAGE As mobile devices become more capable, they’ll need to store a growing amount of data. Getting tiny mobile units to store vast quantities of informa-tion isn’t easy, however, given physical space restraints. But researchers are working hard to pack data into ever-smaller amounts of space. 2.14.1 Tiny Hard Drive Toshiba has developed a 0.85-inch hard disk drive, the first hard drive to deliver multi-gigabyte data storage to a sub-one-inch form factor.The device is suitable for use in a wide range of mobile devices,including palmtops,ultra-portable notebook PCs, handheld GPS units, and digital audio players and jukeboxes. With the new drive, Toshiba has achieved a smaller, lighter, high-capacity storage medium in which low-power consumption is complemented by high performance. The drive will have an initial capacity of 2 to 4GB and deliver enhanced data storage to smaller, lighter more efficient products. Toshiba expects the new drive to bring the functionality and versatility of hard disk drives to a wide range of devices,including mobile phones,digital camcorders, and external storage devices,as well as inspire other manufacturers to develop new applications.The device is scheduled to begin appearing in mobile devices during 2005. Work on the drive has centered on Toshiba’s Ome Operations-Digital Media Network,home to the company’s main development site for digital and mobile products and the manufacturing site for the device. The drive under development is planned to have a capacity of 2 to 4GB, but Toshiba antici-pates achievement of even higher densities in the near future. 2.14.2 Optical Storage A new optical storage medium, developed jointly by engineers at Princeton University and Hewlett-Packard,could profoundly affect the design and capa-bilities of future mobile devices, including mobile phones and PDAs. 58 NUTS AND BITS—TELECOM HARDWARE, SOFTWARE, AND MORE The discovery of a previously unrecognized property of a commonly used conductive polymer plastic coating, combined with very thin-film, silicon-based electronics,is expected to lead to a memory device that’s compact,inex-pensive, and easy to produce. The breakthrough could result in a single-use memory card that permanently stores data and is faster and easier to use than a CD. The device could be very small because it would not involve moving parts such as the laser and motor drive required by CDs. “We are hybridiz-ing,” says Stephen Forrest, the Princeton electrical engineering professor who led the research group. “We are making a device that is organic—the plastic polymer—and inorganic—the thin-film silicon—at the same time.” The device would be like a CD in that writing data onto it makes perma-nent physical changes in the plastic and can be done only once. But it would also be like a conventional electronic memory chip because it would plug directly into an electronic circuit and would have no moving parts.“The device could probably be made cheaply enough that one-time use would be the best way to go,” Forrest says. Hewlett-Packard researcher Sven Möller made the basic discovery behind the device by experimenting with a polymer material called PEDOT, which is clear and conducts electricity.The material has been used for years as an anti-static coating on photographic film and more recently as an electrical contact on video displays that require light to pass through the circuitry.Möller found that PEDOT conducts electricity at low voltages but permanently loses its con-ductivity when exposed to higher voltages and currents, making it act like a fuse or circuit breaker. This finding led the researchers to use PEDOT as a way of storing digital information.A PEDOT-based memory device would have a grid of circuits in which all the connections contain a PEDOT fuse. A high voltage could be applied to any of the contact points, blowing that particular fuse and leaving a mix of working and nonworking circuits. These open or closed connections would represent “zeros” and “ones” and would become permanently encoded in the device. A blown fuse would block current and be read as a “zero,” whereas an unblown one would let current pass and serve as a “one.” The memory circuit grid could be made so small that,based on the test junc-tions the researchers made, 1 million bits of information could fit in a square millimeter of paper-thin material. If formed as a block, the device could store more than one gigabyte of information, or about 1,000 high-quality images, in one cubic centimeter, which is about the size of a fingertip. Developing the invention into a commercially viable product will require additional work on creating a large-scale manufacturing process and ensuring compatibility with existing electronic hardware, a process that might take as few as five years, Forrest says. The technology offers numerous potential mobile device applications. Extensive and detailed street map databases, designed for use with GPS and other location-oriented services, could be easily inserted into even the small-est mobile devices and consume very little power. Other possible applications STORAGE 59 include easily accessible music and e-book libraries, shopping and attraction directories, and powerful software applications. Funding for Forrest’s research came in part from Hewlett-Packard as well as from the National Science Foundation. Princeton University has filed for a patent on the invention.Hewlett-Packard has an option to license rights to the technology. 2.14.3 Nanoring Memory Recent nanotechnology research at Purdue University could pave the way toward faster computer memories and higher density magnetic data storage, all with an affordable price tag. Just like the electronics industry, the data storage industry is on the move toward nanoscale. By shrinking components to below 1/10,000th the width of a human hair,manufacturers could make faster computer chips with more fire-power per square inch. However, the technology for making devices in that size range is still being developed, and the smaller the components get, the more expensive they are to produce. Purdue chemist Alexander Wei may have come up with a surprisingly simple and cheap solution to the shrinking data storage problem. Wei’s research team has found a way to create tiny magnetic rings from particles made of cobalt. The rings are much less than 100nm across—an important threshold for the size-conscious computer industry—and can store magnetic information at room temperature. Best of all, these “nanorings” form all on their own, a process commonly known as self-assembly. “The cobalt nanoparticles which form the rings are essentially tiny magnets with a north and south pole, just like the magnets you played with as a kid,” says Wei, who is an associate professor of chemistry in Purdue’s School of Science.“The nanoparticles link up when they are brought close together.Nor-mally you might expect these to form chains, but under the right conditions, the particles will assemble into rings instead.” The magnetic dipoles responsible for nanoring formation also produce a collective magnetic state known as flux closure.There is strong magnetic force, or flux, within the rings themselves, stemming from the magnetic poles each particle possesses. But after the particles form rings, the net magnetic effect is zero outside. Tripp developed conditions leading to the self-assembly of the cobalt nanorings, then initiated a collaboration with Dunin-Borkowski to study their magnetic properties.By using a technique known as electron holog-raphy, the researchers were able to observe directly the flux-closure states, which are stable at room temperature. “Magnetic rings are currently being considered as memory elements in devices for long-term data storage and magnetic random-access memory,”Wei says.“The rings contain a magnetic field, or flux, which can flow in one of two directions,clockwise or counterclockwise.Magnetic rings can thus store binary 60 NUTS AND BITS—TELECOM HARDWARE, SOFTWARE, AND MORE information, and, unlike most magnets, the rings keep the flux to themselves. This minimizes crosstalk and reduces error during data processing.” When you turn on your computer, it loads its operating system and what-ever documents you are working on into its RAM,or random-access memory. RAM is fast, enabling your computer to make quick changes to whatever is stored there,but its chief drawback is its volatility—it cannot perform without a continuous supply of electricity. Many people have experienced the frustra-tion of losing an unsaved document when their computer suddenly crashes or loses power, causing all the data stored in RAM to vanish. “Nonvolatile memory based on nanorings could in theory be developed,” Wei says. “For the moment, the nanorings are simply a promising develop-ment.”Preliminary studies have shown that the nanorings’ magnetic states can be switched by applying a magnetic field, which could be used to switch a nanoring “bit” back and forth between 1 and 0. But according to Wei, perhaps the greatest potential for his group’s findings lay in the possibility of combin-ing nanorings with other nanoscale structures. “Integrating the cobalt nanorings with electrically conductive nanowires, which can produce highly localized magnetic fields for switching flux closure states,is highly appealing.”he says.“Such integration may be possible by virtue of self-assembly.” Several research groups have created magnetic rings before but have relied on a “top-down” manufacturing approach, which imposes serious limitations on size reduction. “The fact that cobalt nanoparticles can spontaneously assemble into rings with stable magnetic properties at room temperature is really remarkable,”Wei says.“While this discovery will not make nonvolatile computer memory available tomorrow, it could be an important step towards its eventual development. Systems like this could be what the data storage industry is looking for.” Wei’s group is associated with the Birck Nanotechnology Center, which will be one of the largest university facilities in the nation dedicated to nanotechnology research when construction is completed in 2005. Nearly 100 groups associated with the center are pursuing research topics such as nanometer-sized machines, advanced materials for nanoelectronics, and nanoscale biosensors. 2.15 MORE EFFICIENT BASE STATIONS As mobile devices get better,researchers are also looking to improve the tech-nology that handles users’ calls.For example,Cambridge,Massachusetts-based Vanu has created the Vanu Software Radio, a software-based system that promises to replace a mobile phone tower’s room full of communications hardware with a single computer.The system is designed to making personal communications more affordable, particularly for small, rural communities. The software is also capable of running emergency communications—such as ... - tailieumienphi.vn